This invention relates generally to fusing of toner images in an electrostatographic process and more particularly to flash fusing toner images on a receiver member using infrared radiation directed along a path having a major low-angle component relative to such member.
In a typical electrostatographic process, a latent electrostatic charge image on a photoconductive member is developed by contacting the charge image with a colorant (toner) in the form of dry resinous marking particles. The particles are electrostatically charged in an opposite sense to the latent charge image and adhere to the photoconductive member to form a visible imagewise distribution of marking particles corresponding to the latent charge image. The visible imagewise distribution of particles is then transferred to the surface of a receiver member. Subsequently, the transferred particles are fixed (fused) to the receiver member. The fusing operation is accomplished by application of energy (such as heat and/or pressure) or solvent vapor to the particles and the member. The energy, or solvent vapor, at least partially melts the toner particles so that the melted portion adheres to the surface of the member. For example, when the receiver member is a sheet of paper, the melted portion is imbibed into the surface fibers of the sheet. Thus when the particles re-solidify, they are fixed to the sheet.
One method of fusing the marking particles involves directing a burst of radiant energy onto the particles and receiver member; see for example, U.S. Pat. No. 4,205,220 issued May 27, 1980, in the name of O'Brien and assigned to a common assignee. This method, referred to as flash fusing, has had limited commercial application because different energy levels have heretofore been required to adequately fix line images and large area images, making the simultaneous fixing of line and large area images difficult. The apparent reason for needing different energy levels is that the source of radiant energy, at a particular energy level below the level which burns the receiver member, is arranged to direct energy normal to the receiver member. The energy striking the upper portion of marking particle surfaces on the receiver member, is absorbed by the particles but the remainder is reflected or refracted into the environs. A large solid area of particles accumulates sufficient radiant energy from direct and refracted radiation to melt the particles in the solid area. However, small area (line) images or single particles only accumulate direct radiation since the reflected and refracted radiation travels away from the area or particle and is dissapated. Thus, while the top of a particle melts the part in contact with the member does not. Heat loss due to convection cooling at the interface between the particle and the receiver member does not allow sufficient melting of the particle for the particle to adhere to the surface of the receiver member.